Once karcharos sharks reach maturity - approximately 15 years after hatching - they must be moved from their salt water pools to the open ocean and allowed to range free. A karcharos who has been properly taken care of and bonded to their magi will always return, and some magis report that their karcharos will respond to certain patterns of sound or movement in the water, even out on the open ocean. Even as adults, karcharos are inherently mouthy, testing out anything new within their territory with their teeth, even if they don't actually want to eat it. They learn quickly and can not only apply this new-found knowledge to themselves, but are also able to communicate it somehow to clan members or other nearby sharks. While not especially playful, they do seem to enjoy swimming with their magi, and a magi with the right protections against rough shark skin can even go for a ride.

One of the largest shark species in the world, karcharos sharks easily reach over 20 feet long as adults, with rumors of even larger specimens in the areas of the ocean where magis don't often venture. Taking on a karcharos as a companion isn't for those without time and patience; karcharos sharks can live up to 100 years and aren't easily tamed, nor do they take well to new owners. Ancient texts claim that karcharos sharks are gods given shark form so that they can patrol their ocean territory as warriors, and this protectiveness extends to their magi. Due to their size, speed, and teeth, karcharos sharks have very few natural predators other than leviathans, krakens, and occasionally akhluts. Fortunately their territories don't often overlap: karcharos sharks prefer warmer coastal areas, especially around the Callisto Islands. These massive sharks travel all over the world but finding and taking an egg isn't an easy task, as their breeding grounds are very well-hidden and fiercely defended. Some reports indicate that in protecting their nurseries, karcharos sharks can actually jump onto boats, which doesn't often end well for the shark or the people on-board.